1. Field of the invention
The present invention relates to a device for pressing a thermal sensitive head in a thermal print-type color video printer, and more particularly a press device in a thermal print-type color video printer, which is capable of uniformly pressing a printing sheet and a dye film against a thermal sensitive head.
2. Description of the Prior Art
Such a thermal print-type color video printer includes a thermal sensitive head which has a group of heating elements arranged along a transverse axis, so as to accomplish a printing, line by line. In this case, the thermal sensitive head has a substantial length that makes it difficult to contact a platen throughout the length thereof. As a result, it is impossible to press uniformly a printing sheet and a dye film against the thermal sensitive head, thereby causing the printing concentration in each printed line to be irregular.
This disadvantage will now be described, in conjunction with one conventional printing head pressing device illustrated in FIG. 4. As shown in the drawing, the pressing device comprises a first holder 102 and a second holder 102' both fixedly mounted at respective ends thereof on opposite ends of the rear surface (that is, the upper surface in FIG. 4) of a thermal sensitive head 101, by means of screws 107, respectively. At the respective other ends, both holders 102 and 102' have throughout holes 104 through which opposite ends of a shaft 103 fixed to a first support structure 108 extend, respectively. Beneath the thermal sensitive head 101, a platen 105 is rotatably mounted on a second support structure 109, by means of a shaft 106 extending throughout the central axis of the platen 105, such that the outer surface of the platen 105 is in contact with the lower surface of the thermal sensitive head.
In operation, the thermal sensitive head 101 hinges about the shaft 103 so that the lower surface thereof is pressed against the peripheral outer surface of the platen 105, during printing. Between the thermal sensitive head 101 and the platen 105, a dye film 110 and a printing sheet 111 are disposed together, under pressed condition. As the platen 105 rotates about the shaft 106 in a direction indicated by an arrow in FIG. 4, the dye film 110 and the printing sheet 111 are fed in a direction indicated by an arrow in FIG. 4. At this time, the thermal sensitive head 101 applies heat to the dye film 110, according to video signals, so that dye from the dye film 110 adheres to the printing sheet 111. Thus, a printing according to video signals is carried out on the printing sheet, line by line.
However, when the thermal sensitive head 101 is not fully in contact with the platen 105 throughout the length thereof, that is, when the thermal sensitive head 101 is not in contact with the platen 105 at one end thereof, as shown in FIGS. 4A and 4B, a picture printed on the printing sheet 111 by the thermal sensitive head 101 includes a deteriorated portion. This deteriorated picture portion is formed at the area where the thermal sensitive head 101 is not in contact with the platen 105.
In the above-mentioned conventional pressing device, it is difficult for the thermal sensitive head 101 to be in contact with the platen 105 uniformly throughout the length thereof, due to tolerance in manufacture and wear and friction occurring in use.